Comportamento térmico de argamassas de fachada

Abstract

In civil construction, there are many possible pathological manifestations in a building, particularly on mortar surfaces, such as cracks and infiltrations. The origins of these damages vary widely, either by the use of low-quality materials, overloading, failure in construction or the climate action. Furthermore, it is worth mentioning that those damages can make the elements of the building debilitate their functions, in some cases, putting the lives of its users at risk, as in the case of displacement of mortar surfaces. For façade mortars, weather has the potential to deteriorate performance at an accelerated rate. It is usual to relate the effects of thermal amplitude and consequent thermal stresses with the accelerated deterioration of sunny façades, due to the phenomenon of fatigue. However, there is no established procedure to assess such risk. That said, this work aims to investigate the thermal behavior of mortars on sunny façades. While a simplified calculation of fatigue is presented as a justification of the risk of thermal fatigue (considering thermal amplitudes, modulus of elasticity, coefficient of thermal expansion and Wöhler curve from the literature), the work focuses on the measurement of thermal amplitudes in real facades and the validation of a finite element model for thermal calculation. An experimental temperature curve of the mortar façade as a function of time was obtained, for the duration of one day, aiming at the determination of a daily thermal amplitude. The thermal amplitudes measured on a 50-cm by 50-cm mortar surface, 2.5-cm thick, were approximately 26℃ for facades with natural colors and 40℃ for darker facades, measurements being obtained on sunny days in the city of FortalezaCE, on a vertical wall positioned at 0ºN, on the west side of the wall. The results of the finite element model built to evaluate the thermal behavior of façades with different levels of insolation were compared with the experimental results, adjusting the parameters of convective heat exchange coefficient and surface absorbance (values approximately 97.80% for dark colorings and 10.20% for light colorings), with satisfactory results. Values of wind speed, air temperature and insolation in the study region, provided by INMET, were considered as input parameters. That said, a path for estimating durability in regard to thermal fatigue is presented, with 3 main steps: (i) prediction of thermal amplitudes as a function of the color of the mortar surface; (ii) carrying out Young’s modulus tests; (iii) carrying out fatigue tests. This work focused on item i.